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    <H1 CLASS="title">Class Template <CODE>basic_line_filter</CODE></H1>
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<DL class="page-index">
  <DT><A href="#description">Description</A></DT>
  <DT><A href="#headers">Headers</A></DT>
  <DT><A href="#reference">Reference</A></DT>
  <DT><A href="#example">Example</A></DT>
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<A NAME="description"></A>
<H2>Description</H2>

<P>
    The class template <CODE>basic_line_filter</CODE> is a <A HREF='../concepts/dual_use_filter.html'>DualUseFilter</A> for use as a base class by Filters which filter a character sequence one line at a time. Derived classes override the <CODE>private</CODE> <CODE>virtual</CODE> function <CODE>do_filter</CODE>, which takes a line of unfiltered text as argument returns the result of filtering the line.
</P>

<A NAME="headers"></A>
<H2>Headers</H2>

<DL class="page-index">
  <DT><A CLASS="header" HREF="../../../../boost/iostreams/filter/line.hpp"><CODE>&lt;boost/iostreams/filter/line.hpp&gt;</CODE></A></DT>
</DL>

<A NAME="reference"></A>
<H2>Reference</H2>

<H4>Synopsis</H4>

<PRE CLASS="broken_ie"><SPAN CLASS="keyword">namespace</SPAN> boost { <SPAN CLASS="keyword">namespace</SPAN> iostreams {

<SPAN CLASS='keyword'>template</SPAN>&lt;<SPAN CLASS='keyword'>typename</SPAN> <A CLASS='documented' HREF='#template_params'>Ch</A>, <SPAN CLASS='keyword'>typename</SPAN> <A CLASS='documented' HREF='#template_params'>Alloc</A> = std::allocator&lt;Ch&gt; &gt;
<SPAN CLASS='keyword'>class</SPAN> <A CLASS='documented' HREF='#template_params'>basic_line_filter</A>  {
<SPAN CLASS='keyword'>public:</SPAN>
    <SPAN CLASS='keyword'>typedef</SPAN> Ch                                char_type;
    <SPAN CLASS='keyword'>typedef</SPAN> std::basic_string&lt;
                Ch, 
                std::char_traits&lt;char_type&gt;,   
                Alloc
            &gt;                                 string_type;
    <SPAN CLASS='keyword'>typedef</SPAN> <SPAN CLASS='omitted'>[implementation-defined]</SPAN>          category;
<SPAN CLASS='keyword'>protected:</SPAN>
    basic_line_filter();
<SPAN CLASS='keyword'>public:</SPAN>
    <SPAN CLASS='keyword'>virtual</SPAN> ~basic_line_filter();
<SPAN CLASS='keyword'>private:</SPAN>
    <SPAN CLASS='keyword'>virtual</SPAN> string_type <A CLASS='documented' HREF='#do_filter'>do_filter</A>(<SPAN CLASS='keyword'>const</SPAN> string_type&amp; line) <SPAN CLASS='numeric_literal'>= 0</SPAN>;
};

<SPAN CLASS='keyword'>typedef</SPAN> basic_line_filter&lt;<SPAN CLASS='keyword'>char</SPAN>&gt;     <SPAN CLASS='defined'>line_filter</SPAN>;
<SPAN CLASS='keyword'>typedef</SPAN> basic_line_filter&lt;<SPAN CLASS='keyword'>wchar_t</SPAN>&gt;  <SPAN CLASS='defined'>wline_filter</SPAN>;

} } <SPAN CLASS="comment">// End namespace boost::io</SPAN></PRE>

<A NAME="template_params"></A>
<H4>Template parameters</H4>

<TABLE STYLE="margin-left:2em" BORDER=0 CELLPADDING=2>
<TR>
    <TR>
        <TD VALIGN="top"><I>Ch</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
        <TD>The <A HREF='../guide/traits.html#char_type'>character type</A></TD>
    </TR>
    <TR>
        <TD VALIGN="top"><I>Alloc</I></TD><TD WIDTH="2em" VALIGN="top">-</TD>
        <TD>A standard library allocator type (<A CLASS="bib_ref" HREF="../bibliography.html#iso">[ISO]</A>, 20.1.5), used to allocate a character buffer</TD>
    </TR>
</TABLE>

<A NAME="do_filter"></A>
<H4><CODE>line_filter::do_filter</CODE></H4>

<PRE CLASS="broken_ie">    <SPAN CLASS='keyword'>virtual</SPAN> string_type do_filter(<SPAN CLASS='keyword'>const</SPAN> string_type&amp; line) <SPAN CLASS='numeric_literal'>= 0</SPAN>;</PRE>

<P>The argument <CODE>line</CODE> represents a single line of unfiltered text, not including any terminal newline character. Returns the result of filtering <CODE>line</CODE>.</P>

<A NAME="example"></A>
<H2>Example</H2>

<P>The following example shows a <CODE>line_filter</CODE> which counts the number of lines which exceed a given length.</P>

<PRE CLASS="broken_ie"><SPAN CLASS='preprocessor'>#include</SPAN> <A CLASS='header' HREF='../../../../boost/iostreams/filter/line.hpp'><SPAN CLASS='literal'>&lt;boost/iostreams/filter/line.hpp&gt;</SPAN></A>

<SPAN CLASS='keyword'>namespace</SPAN> io = boost::iostreams;

<SPAN CLASS='keyword'>class</SPAN> long_line_counter : <SPAN CLASS='keyword'>public</SPAN> io::line_filter {
<SPAN CLASS='keyword'>public</SPAN>
    <SPAN CLASS="keyword">explicit</SPAN> long_line_counter(<SPAN CLASS='keyword'>int</SPAN> max_length = <SPAN CLASS='numeric_literal'>80</SPAN>) 
        : max_(max_length), count_(<SPAN CLASS='numeric_literal'>0</SPAN>) 
        { }
    <SPAN CLASS='keyword'>int</SPAN> count() <SPAN CLASS='keyword'>const</SPAN> { <SPAN CLASS='keyword'>return</SPAN> count_; }
<SPAN CLASS='keyword'>private:</SPAN>
    std::string do_filter(<SPAN CLASS='keyword'>const</SPAN> std::string&amp; line)
    {
        <SPAN CLASS='keyword'>if</SPAN> (line.size() &gt; max_)
            ++count_;
    }
    <SPAN CLASS='keyword'>int</SPAN> max_;
    <SPAN CLASS='keyword'>int</SPAN> count_;
};</PRE>

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    Distributed under the Boost Software License, Version 1.0. (See accompanying file LICENSE_1_0.txt or copy at <A HREF="http://www.boost.org/LICENSE_1_0.txt">http://www.boost.org/LICENSE_1_0.txt</A>)
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